Liquid crystals have been used to display information in flat-panel displays for many years, such as are commonly used in watch faces or half page size displays for lap-top computers and the like.
Liquid crystal displays made up of bistable chiral nematic materials do not require continuous updating or refreshing. When data or information changes on the display, the electronics update the display. If, however, the display information does not change, the display can be written once and remain in its information-conveying configuration for extended periods without display processor intervention. The ability to remain in a stable state for an extended period has resulted in use of chiral nematic liquid crystal displays for signs that can be slowly updated over relatively long periods of time. Since the display information does not change, the fact that it may take longer to write the initial information to the display is not important.
A number of prior art patents disclose techniques for updating liquid crystal display information. So-called liquid crystal display drivers or electronic circuits are known in the prior art and utilize various techniques for updating a liquid crystal display. U.S. Pat. No. 5,251,048 which issued Oct. 5, 1993 to Doane et al. concerns a method and apparatus for electronic switching of a reflective color display system. This patent discloses use of a liquid crystal light-modulating material that is confined between substrates. Elongated conductive paths supported on opposite sides of the substrates activate picture elements at controlled locations to set up a display screen. The disclosure of the '048 patent to Doane et al. is incorporated herein by reference.
A paper entitled "Storage Type Liquid Crystal Matrix Display" to Tani et al. (SID 79 Digest, p. 114-115) proposes a liquid crystal display driver system whose operation takes into account transitions between various states of a chiral nematic liquid crystal material. The paper describes a storage type liquid crystal display having the advantages of long storage time which makes refreshing or updating of the information on the display unnecessary. However, the Tani et al. drive scheme is limited in its resolution and information density conveying ability. His drive waveform and technology are limited in the number of lines that can be addressed to roughly 100 lines, far less than the 1000 lines required for page size viewer applications. Also, his demonstrated writing times of greater than 8 milliseconds (ms.) per line are insufficient for commercially acceptable page size viewers. On a flat-panel display or the like, 100 lines of information in a liquid crystal display is not acceptable for conveying text and 8 ms. per line is far too slow for many applications.
In the invention disclosed in U.S. application Ser. No. 08/390,068, filed Feb. 17, 1995 and entitled "Dynamic Drive Method and Apparatus For a Bistable Liquid Crystal Display," a method and display driver circuitry for speeding the rate of updating a 1,000 row cholesteric liquid crystal display was disclosed. Application Ser. No. 08/390,068 is incorporated herein in its entirety by reference. An updating time of approximately one second for a 1000 row cholesteric liquid crystal display was achieved. By simultaneously addressing multiple rows of the display with a pipelining scheme, the overall updating time for the display was kept at one second.